As Onyx Pharma soars on a takeover bid - and the possibility of a higher offer - rival cancer drug maker Celgene may offer more upside.

Onyx (ticker: ONXX) shares skyrocketed 51% to $131 in afternoon trading following the revelation this weekend that the company rejected an unsolicited offer from Amgen (AMGN) for $120 a share as too low. Management has now told the company's investment banker to shop Onyx around to other potential buyers.